Waterproof, moisture-vapor permeable materials have been developed which find use in garments and tents which do not leak when contacted or flexed and which are permeable to moisture such as perspiration.
U.S. Pat. No. 4,194,041 (Gore et al) incorporated by reference herein, is representative of a number of patents which describe coatings or laminates purported to provide waterproof articles which do not leak when touched and are breathable. This patent describes a layered article for use in waterproof garments or tents comprising at least two layers: an interior, continuous hydrophilic layer that readily allows water to diffuse therethrough, prevents the transport of surface active agents and contaminating substances such as those found in perspiration, and is substantially resistant to pressure induced flow of liquid water, and a hydrophobic layer that permits the transmission of water vapor and provides thermal insulating properties even when exposed to rain. The hydrophobic layer is preferably waterproof microporous tetrafluoroethylene (PTFE) or polypropylene, which permits the passage of moisture vapor through the pores thereof. The hydrophilic layer transfers moisture vapor therethrough whereupon it passes through the porous hydrophobic layer. Various means of joining the layers are suggested including the application of hydraulic pressure to force the hydrophilic polymer to penetrate into the surface void spaces of the hydrophobic layer.
U.S. Pat. No. 4,443,511 (Worden et al) incorporated by reference herein, discloses a layered article similar to that of U.S. Pat. No. 4,194,041, but formed of a breathable polytetrafluoroethylene first layer mechanically stretched at least about 5% beyond its yield point having a surface layer of elastomeric hydrophilic material having a surface in interlocking relationship with the inner face of the first layer. The interlocking relationship is said to be brought about by flowing the hydrophilic elastomeric material into the layer of hydrophobic material and then solidifying the hydrophilic material.
U.S. Patent No. 4,613,544 (Burleigh) (assigned to the assignee of the present case) incorporated by reference herein, discloses a waterproof, moisture-vapor permeable unitary sheet material which comprises a microporous polymeric matrix having pores comprising continuous passages extending through its thickness and opening into the opposite surfaces thereof, the passages being sufficiently filled with moisture-vapor permeable water-impermeable, hydrophilic material to prevent the passage of water and other liquids through the unitary sheet material while readily permitting moisture vapor transmission therethrough rendering the sheet material breathable.
A number of hydrophilic materials are susceptible to degradation. A particularly harmful type of degradation is autoxidative degradation. In addition to transition group metals, this degradation is catalyzed by chloride ion. Hindered phenolic antioxidants prevent the degradation of such materials. Thus, in order to protect such materials from salts contained in perspiration, etc., such antioxidants have been physically blended into the hydrophilic materials. Antioxidants compatible with the hydrophilic material have solubility characteristics which render them soluble in organic solvents. Consequently, these antioxidants can be extracted by contact with dry cleaning solvents over time. After removal of the antioxidant the breathable membranes experience increased susceptibility to degradation from salts contained in perspiration, etc. Hindered phenolic antioxidants which have been blended with hydrophilic materials in order to provide moisture-vapor permeable materials such as those available from Ciba Geigy Corporation under the trade designations Irganox 1010 and Irganox 1076 do not have reactive functionalities that would enable them to be directly reacted into the structure of a hydrophilic urethane polymer. Other antioxidants (i.e. hindered phenolic amide alcohols) exist which have been reacted into nonhydrophilic materials. Such nonhydrophilic modified polymers would not be useful in preparing waterproof breathable membranes. In addition, such antioxidants are not easy to prepare.
A need thus exists for a moisture-vapor permeable, water-impermeable hydrophilic polymer which is resistant to degradation from salts.
A need also exists for a waterproof breathable material which contains an antioxidant which does not leach out upon being subjected to dry cleaning solvents and which experiences the same good moisture vapor transmission rate as known materials.
A need also exists for a hindered phenolic antioxidant which is easy to prepare which can be reacted into the structure of a hydrophilic polymer. We have found such a polymer, such an antioxidant, and such a material.